1. Field of the Invention
The present invention relates generally to digital camera, and more particularly, to a lens module for a digital camera.
2. Discussion of the Related Art
Generally, digital cameras are image recording media capable of photographing a plurality of still images without using film. Such a digital camera typically uses an image pickup device, which is a kind of semiconductor device, such as a charge coupled device (CCD) or complementary metal oxide semiconductor (CMOS). In the digital camera, an object image formed on the image pickup device through a lens is converted into an electrical signal by the image pickup device, and the electrical signal is stored as a digital signal.
However, the color spectrum seen by a CCD or CMOS camera is much wider than the spectrum seen by the human eye. Especially in the near infrared region of the spectrum the difference in sensitivity is significant. Since many light sources, including the sun, emit infrared light, a CCD or CMOS camera in daylight will therefore see a significant amount of infrared light resulting in strange colors. Therefore, many lenses need to be designed with an IR-cut filter. The IR-cut filter may block the transmission of the infrared light while passing the visible light.
A typical lens for a digital camera is represented in FIG. 2. The lens includes an aperture stop 81, a first lens element 82, a field stop 83, a second lens element 84, an IR-cut filter 85 and a CMOS image sensor 86. The first lens element 82 and the second lens element 84 are made of plastic, and are aspheric lens elements. The light reflected from an image object passes through the first lens element 82 and the second lens element 84. The light is then focused and then passes through the IR-cut filter 85. The light then arrives at the CMOS image sensor 86. The aperture stop 81 can adjust the quantity of the light entering from the outside. The field stop 83 can control the quantity of the light entering the CMOS image sensor 86. The IR-cut filter 85 filters the infrared rays from the light. Although the lens is light and does not easily break owing to using plastic lens elements, the first lens element 82 is located at the front, and is easily scraped or abraded which can effect the image quality.
Therefore, a digital camera with a new lens module is desired in order to overcome the above-described shortcomings.